1. Field of the Invention
This invention relates to a new heat engine particularly adaptable for use with water as a working fluid and producing useful energy by the pulse-jet principle.
2. Description of the Prior Art
In boat propulsion, it is conventional to start with a source of energy, e.g., fuel, which produces heat energy and to impart kinetic energy to the ambient water, so that the boat will be pushed forward by reaction. It is usual to have a great deal of machinery between these two extremes. For example, the fuel heats water in a boiler to make steam, which drives a turbine, which drives a water propeller via a gearbox, which develops a reactive thrust. In the present invention, the heat is applied directly to the ambient water in order to achieve the same effect, thus eliminating the intervening machinery. A known propulsive unit of this general type was patented by McHugh in 1916 (U.S. Pat. No. 1,200,960) and the principle of his engine is illustrated in FIG. 1. Assuming that there is initially some water in the boiler, the heat turns it to steam and pushes the ambient water interface down the tube. When all the water in the boiler has been turned to steam, the steam condenses in the cool section of the pipe, the pressure drops, and the water interface moves back toward the boiler. When it reaches the boiler, some water splashes in, and because the tube is raised above the floor of the boiler, this splashed water is trapped and is again turned to steam, pushing the interface down the tube. A net thrust force to the left is produced, principally because when the ambient water is flowing into the tube, it comes from all directions (a "sink" flow) while when it emerges, it comes out as a jet, because finite fluid viscosity prohibits "source" flows from a pipe (see FIG. 2b). Numerous other later patents all operate on the same principle of trapping a small quantity of water in the boiler at the end of each induction phase.
McHugh's invention was specifically for a toy boat, and most of the following inventors specify or imply the same application. It was recognized that the principle could not be scaled up to "full scale" boats principally because many people had attempted to accomplish this, particularly in the early 1920's without success. There were two key reasons for this inability to scale up the phenomena. Firstly, the steam-water interface, shown in FIG. 1, was preserved by surface tension, and this is only possible in very small diameter tubes. In larger tubes, there was no stable interface, and the steam bubbled into the ambient water and was condensed without moving the bulk of the water in the tube. More importantly, even if this problem has been solvable, the pressures developed were inherently low so that there was no possibility of achieving efficient operation.
Also, U.S. Pat. No. 3,013,384 disclosed a device of general interest in which the tubular member is not closed at one end but has a water injector. Water is passed through the tube which contains pulse arc means therein to heat the fluid itself. The working fluid does not oscillate within the tube, but rather is injected, vaporized and expanded.